There is an increasing demand for accurate portable eye trackers and fixation monitors. Since eye gaze is a strong indication for current attention and intention, such a device may automatically and accurately estimate: where the person is looking, the current and past areas of attention, the possible intentions of the person, and the possible mental state of a person. Eye tracking thus provides a key input to enable a range of applications and devices that would benefit from utilizing such information. The scope of potential applications is extensive, ranging from medical diagnostics to intuitive and fast computer interfacing. Examples include mobile devices, computer interaction in professional environments, clinical diagnostics, security applications, vehicle security and vehicle interaction, computer gaming, etc. Presently, eye tracking already provides great value in commercial and research-related applications such as psychology and vision research, commercial usability and advertising studies, and eye-based communication for people with highly limited mobility, etc.
Eye position can be estimated by a variety of techniques, each of them having its advantages and limitations. While the purpose of an eye tracker is to identify where a person is looking, most contemporary eye trackers detect eye position, usually employing the reflection of a point light source from the front of the cornea (corneal light reflex) relative to the bright or dark pupil, or relative to the reflection of the same point light source from the back of the crystalline lens of the eye (fourth Purkinje image). These and other similar techniques monitor the position of the globe itself, and not the actual visual axis or point of fixation. When an individual looks at a target, that target is imaged on the fovea. It is thus foveal fixation that correlates precisely with gaze direction. Our recent research has shown that techniques which effectively track or monitor the optical projection of fundus landmarks out from the eye afford a more direct measurement of fixation direction, are physiologically more relevant, and can achieve high precision. It has also been shown that landmarks such as the fovea and the optic disc can be detected robustly by measuring the amount of polarization change that the surrounding birefringent nerve fibers cause during double passage of a beam of polarized light through them upon fundus reflection in double-pass systems. Polarized near-infrared light is reflected from the foveal and optic disc areas in bow-tie or propeller patterns of polarization states. For any particular eye and particular type of polarized light used, the pattern of reflected polarization states is of constant shape, size, and location relative to the direction of that eye's fixation and are therefore detectable, offering the opportunity for precise eye tracking. An advantage of this new eye-fixation detection and tracking method can include that it uses true information coming directly from retinal landmarks, as opposed to existing eye-tracking systems which use reflections from other structures, to identify the direction of foveal gaze.
As noted above, while the purpose of an eye tracker is to identify where a person is looking, most contemporary eye trackers detect eye position, usually employing the reflection of a point light source from the front of the cornea (corneal light reflex) relative to the bright or dark pupil, or relative to the reflection of the same point light source from the back of the crystalline lens of the eye (fourth Purkinje image). These and other similar techniques monitor the position of the globe itself, and not the actual visual axis or point of fixation. When an individual looks at a target, that target is imaged on the fovea. It is thus foveal fixation that correlates precisely with gaze direction. We have previously developed eye fixation monitors that use foveal information, employing moving parts to scan the area around the fovea. However, moving parts can lead to cost and reliability issues, as well as difficultly in compactly incorporating such optoelectronic systems into many devices.
There thus remains a need for improved eye tracking and gaze fixation detection systems, methods and components.